The present invention relates to a manoeuvrable trailing dredging vessel, like a trailing suction hopper dredger (TSHD), comprising a vessel propulsion member coupled with a propulsion shaft for driving the propulsion member, and a drive system having a central drive shaft for providing power to the vessel propulsion member.
Such a trailing suction hopper dredger (TSHD) has two main sailing modes: 1) free sailing and 2) dredging with a drag head overboard—in short “trailing”. During trailing it is known for a TSHD with controllable pitch propeller (CPP) to vary the propeller thrust by changing the pitch of the CPP blades. The engine (and propeller) speed then stays constant or at least may vary within a small range of speed. This thus almost constant engine speed is essential when driving a shaft generator to be able to supply enough power to electric consumers onboard of the TSHD, or when driving a dredge pump or jet pump(s).
In trailing mode, it is a given that the thrust needed from the propulsion system will change constantly. This is caused by factors like changing current speed and direction, water depth, drag head resistance etc. In general for a TSHD the trailing mode has the highest power consumption and therefore the trailing mode is decisive for the choice of the engine. With a controllable pitch propeller (CPP) in trailing mode the pitch of the propeller blades are varied. This results in a (much) lower efficiency of the propeller.
With a fixed pitch propeller (FPP) the propeller speed will be reduced by reducing engine speed when trailing. But however by reducing the engine speed the available engine power is also reduced significantly, which is undesirable.
CN 202 209 384 U discloses a marine gearbox. However, the propulsion shaft is not freely accessible because at least the drive shaft is arranged in line with the propulsion shaft.
JP S58 54258 A relates to a marine speed reduction reversing gear according to its title. Again, the propulsion shaft 25 is not freely accessible at its end as is clear from FIG. 3.